1. Field of the Invention
The present invention relates to a radar system of emitting an electric wave and receiving a reflected wave, thereby detecting a target, and more specifically to a high-resolution pulse radar apparatus which is a pulse radar for emitting a high-frequency transmission electric wave normally after sectioning the electric wave at equal intervals in a pulse form, and is used for short-distance measurement.
2. Description of the Related Art
Most of the current radar units are pulse radar units. A pulse radar generally detects a target in the distance, and measures the distance to the target. Various signal processing technologies for use by such pulse radar units are described in the literature “Radar Signal Processing Technology” by Matsuo Sekine of Institute of Electronics, Information and Communication Engineers.
The conventional technology for detecting a target at a relatively short distance is disclosed by the literature “A Method of Measuring Distance and Velocity of Short-distance Mobile Object”, '00 B-2-2, p. 215, by Morigami and Nakatsukasa at Convention of Institute of Electronics, Information and Communication Engineers. In this literature, a method of measuring the distance and the velocity of a mobile object located within the distance of 125 m using a microwave of 9.5 GHz amplitude-modulated by a sine wave signal.
The Japanese Patent Application Laid-open No. 2001-116822 discloses a small, low-cost, and low power consumption microwave band pulse transmission/reception apparatus applied for use in data communications, sensors, measures, etc. using a weak microwave band radio. A gate is used in this application, but it is to suppress oscillation, and has a purpose different from that of the present invention.
The Japanese Patent Application Laid-open No. 2000-241535 discloses a high-resolution short-distance radar which can be used by a simple license application, can be used outdoors without electric wave interference, and is expected to be widely used in a noncontact distance measurement.
As described above, the conventional pulse radar has been used in measuring a relatively long distance such as several tens of meters to a target. To use a pulse radar in measuring a short distance, it is necessary to obtain a sharp pulse, a wide frequency band, and also a wide band for an element of the device, but it is difficult to satisfy these conditions.
FIGS. 1 and 2 are explanatory views of available bands of the pulse radar. FIG. 1 is an explanatory view of an available band for common AM and FM signals. The available band of AM and FM signals are limited to a narrow band around the frequency of a carrier wave, thereby reducing the influence of noise.
FIG. 2 is an explanatory view of a band of a pulse radar. The narrower the pulse width of a pulse radar, the broader the available band. Therefore, using normal signal power S, the noise power N of the entire band becomes large, the S/N (signal to noise ratio) is lowered, and the system is subject to the influence of noise. The S/N ratio is specifically deteriorated at above 1 GHz, and various undesired problems occur. If the pulse radar width is extended to reduce the S/N ratio, then the band becomes narrower and the noise N is reduced, but the shortest distance to a target to be detected becomes longer.
To set the short-distance limit to approximately 15 cm in detecting a target in the conventional technology of a pulse radar as described above, it is necessary to set the pulse width of about 1 nsec. To attain this, a band width of about 1 GHz is required, and the band width of noise becomes considerably broad, that is, about 1 GHz, thereby lowering the S/N ratio and making the detection of a target more difficult.
Furthermore, since a signal with a pulse width of about 1 nsec, and a frequency band width of about 1 GHz is used, a general-purpose digital LSI such as a DSP, etc. cannot be used, and a circuit has to be configured by a semiconductor exclusively developed for a high-speed use, the system is costly and the properties fluctuate, thereby making it difficult to realize mass production.
Another problem with the conventional technology is that the interference by a plurality of radar units can detect other targets than a target to be detected. That is, a malfunction of detecting wrong targets occurs.